Many industrial processes employ furnaces wherein fuel and oxidant are combusted to generate heat which is used to heat a charge within the furnace. Among such industrial processes one can name glassmaking wherein the charge is glassmaking materials or molten or solid glass, steelmaking wherein the charge is steel or iron and aluminum melting wherein the charge is aluminum ingots or scrap.
In carrying out such furnace combustion it is desirable to completely combust the fuel within the furnace as this serves to maximize the amount of heat released within the furnace and available to heat the charge. Accordingly, oxidant and fuel may be provided into the furnace in a ratio which is not substoichiometric since a substoichiometric ratio would cause some of the fuel to remain unburned or would result in the generation of significant amounts of products of incomplete combustion such as carbon monoxide, hydrocarbons and carbon.
At first glance it would appear that the optimum ratio for providing oxidant and fuel into a furnace for combustion is one that is substantially stoichiometric. However, in practice, such firing leads to some incomplete combustion because of less than perfect mixing of fuel and oxidant within the furnace and also because the reaction kinetics of the fuel and oxidant may not enable all of the fuel to completely combust prior to exiting the furnace. Accordingly, in actual industrial practice, furnaces of this type are operated with excess oxygen to ensure the complete combustion of the fuel within the furnace. Unfortunately, when furnaces are operated in this way, i.e., where oxidant and fuel are provided into the furnace in a superstoichiometric ratio, there arises the tendency to generate excessive levels of nitrogen oxides (NO.sub.x) because oxygen in excess of that needed to react with the fuel becomes available to combine with nitrogen to form NO.sub.x. NO.sub.x is a significant pollutant and there exists a need to reduce the amount of NO.sub.x generated when carrying out combustion.
Accordingly, it is an object of this invention to provide a method for carrying out essentially complete combustion to generate heat efficiently within a furnace to heat a charge while avoiding the generation of high Levels of NO.sub.x.